Wireless communication device and system

ABSTRACT

A wireless communication device according to an embodiment includes a transceiver and a timer. The transceiver transmits and receives data and transmits the data in a first direction and a second direction. The timer determines a timing for the transceiver to transmit data such that a transmission interval in the first direction is longer than a transmission interval in the second direction.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2015-043460, filed on Mar. 5,2015, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a wirelesscommunication system and system.

BACKGROUND

In the related art, wireless communication systems, where multiplewireless nodes are connected to each other in a mesh-like manner, are inuse. As a communication scheme for such wireless communication systems,for example, a time division communication system is employed. In thetime division communication system, timings for the respective wirelessnodes to go to sleep can be easily controlled, and thus, the power ofthe wireless communication systems can be saved.

However, in the time division communication system of the related art,uplink and downlink transmission are performed at the same frequency.Due to this, when a transmission frequency required for uplink and thatrequired for downlink are different, excessive data transmission isperformed, thereby disadvantageously increasing power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a configuration of a wirelesscommunication system according to a first embodiment;

FIG. 2 is a diagram showing FIG. 1 in the form of a network topology;

FIG. 3 is a diagram describing a time division communication system;

FIG. 4 is a diagram describing a slot allocation method according to thefirst embodiment;

FIG. 5 is a diagram describing a slot allocation method according to thefirst embodiment;

FIG. 6 is a diagram describing a slot allocation method in a simplexcommunication frame;

FIG. 7 is a diagram describing a slot allocation method in a duplexcommunication frame;

FIG. 8 is a diagram describing a slot allocation method in a duplexcommunication frame;

FIG. 9 is a diagram describing a slot allocation method in a duplexcommunication frame;

FIG. 10 is a diagram describing a slot allocation method in a duplexcommunication frame;

FIG. 11 is a diagram describing a method of setting transmissionintervals;

FIG. 12 is a diagram showing a functional configuration of a wirelesscommunication device according to the first embodiment;

FIG. 13 is a diagram describing operation timings of a transceiver;

FIG. 14 is a block diagram showing a hardware configuration of awireless communication device;

FIG. 15 is a flowchart showing operations of the wireless communicationdevice in a simplex communication frame;

FIG. 16 is a diagram showing an example of operations of the wirelesscommunication device in a simplex communication frame;

FIG. 17 is a flowchart showing operations of the wireless communicationdevice in a duplex communication frame;

FIG. 18 is a diagram showing an example of operations of the wirelesscommunication device in a duplex communication frame;

FIG. 19 is a diagram showing another example of operations of thewireless communication device in the duplex communication frame;

FIG. 20 is a diagram showing another example of operations of thewireless communication device in a simplex communication frame;

FIG. 21 is a diagram showing another example of operations of thewireless communication device in the simplex communication frame;

FIG. 22 is a state transition diagram showing operation states of awireless communication device according to a second embodiment;

FIG. 23 is a diagram showing operations of the wireless communicationdevice in state 1;

FIG. 24 is a diagram showing operations of the wireless communicationdevice in state 2; and

FIG. 25 is a diagram showing operations of the wireless communicationdevice in state 3.

DETAILED DESCRIPTION

Embodiments will now be explained with reference to the accompanyingdrawings. The present invention is not limited to the embodiments.

A wireless communication device according to an embodiment includes atransceiver and a timer. The transceiver transmits and receives data andtransmits the data in a first direction and a second direction. Thetimer determines a timing for the transceiver to transmit data such thata transmission interval in the first direction is longer than atransmission interval in the second direction.

(First Embodiment)

First, a wireless communication system according to a first embodimentwill be described with reference to FIGS. 1 to 21. FIG. 1 is a diagramshowing an exemplary configuration of the wireless communication systemaccording to the present embodiment. As shown in FIG. 1, this wirelesscommunication system includes a plurality of wireless communicationdevices 1 and a concentrator 2. The wireless communication systemincludes a wireless mesh network, where the wireless communicationdevice 1 is a wireless node and the concentrator 2 is a root node, andcommunicates according to a time division communication system.

In this wireless communication system, the wireless communication device1 and the concentrator 2, arranged within a predetermined range ofdistance, can wirelessly communicate with each other. The wirelesscommunication device 1 is mounted with a sensor such as a temperaturesensor and an acceleration sensor and wirelessly transmits data measuredby the sensor. The data transmitted by the respective wirelesscommunication devices 1 is transmitted via another wirelesscommunication device, or directly, to the concentrator 2. Theconcentrator 2 concentrates data transmitted by the respective wirelesscommunication devices. The concentrator 2 is, for example, a serverprovided with a wireless communication function.

FIG. 2 is a diagram schematically showing the wireless communicationsystem in FIG. 1 in the form of a network topology. In FIG. 2, analphabetical letter indicates the wireless node (wireless communicationdevice 1) and “ROOT” indicates the root node (concentrator 2). In thefollowing description, the wireless communication device and theconcentrator 2 are referred to as a wireless node X and the root node,respectively. X corresponds to an alphabetical letter in the drawings.

When seen from a wireless node X, the direction toward the root node(where the number of hops to the root node is smaller) is referred to asupstream, and the direction away from the root node (where the number ofhops to the root node is larger) is referred to as downstream.Furthermore, an upstream wireless node or the root node, transmitting orreceiving data to or from the wireless node X, is referred to as aparent node and a downstream wireless node, transmitting or receivingdata to or from the wireless node X, is referred to as a child node. Anarrow in FIG. 2 shows a relationship between the wireless nodes. Anarrow runs from a child node and points at a parent node. For example,in FIG. 2, a parent node of a wireless node B is the root node and childnodes of the wireless node B are wireless nodes E, F, and G.

Also, transmission, by the wireless node X, of data received from achild node (parent node) to a parent node (child node) is referred to asrelay. Relay includes transmission of data received by the wireless nodeX while adding data of the wireless node X such as sensor data thereof.Furthermore, transmission of data from downstream to upstream (a firstdirection) is referred to as uplink transmission and transmission ofdata from upstream to downstream (a second direction) is referred to asdownlink transmission.

FIG. 3 is a diagram describing a time division communication system. Inthe time division communication system, an operation time per cycle in awireless communication system is predetermined. This operation time isreferred to as a frame. The wireless communication system operates byrepeating this frame.

Each frame is time-divided into a plurality of slots. Each slot isallocated to one or more wireless nodes. The wireless node transmitsdata during a slot allocated thereto. For example, in FIG. 3, a firstslot is allocated to a wireless node C, a third slot is allocated to awireless node A, and a fifth slot is allocated to a wireless node B. Inthis case, the wireless node C transmits data during the first slots ofthe respective frames. Note that, the frame may include a slot notallocated to the wireless node.

Hereinafter, a slot allocation method in the wireless communicationsystem according to the embodiment will be described with reference toFIGS. 4 to 10. FIGS. 4 and 5 are diagrams describing the slot allocationmethod according to the embodiment. In FIGS. 4 and 5, examples ofwireless mesh networks and slots allocated to the respective wirelessnodes for uplink transmission are shown.

In the wireless mesh network in FIG. 4, an earlier slot in a frame isallocated to a wireless node located later in a pathway of datacommunication. Specifically, when the pathway of data communication froma wireless node V includes wireless nodes V, R, N, L, I, E, B, and theroot node, slots are allocated to the root node, the wireless nodes B,E, I, L, N, R, and V, in the order mentioned.

When the slots are allocated in this manner, a latency t1 where datatransmitted by the wireless node V is relayed by the wireless node R isapproximately one frame. Also in the subsequent respective wirelessnodes, similar latencies occur. Therefore, in the wireless mesh networkin FIG. 4, a data transfer time where the data transmitted by thewireless node V is transferred to the root node is a few frames.

On the other hand, in the wireless mesh network in FIG. 5, an earlierslot in a frame is allocated to a wireless node located earlier in apathway of data communication. Specifically, when the pathway of datacommunication from a wireless node V includes wireless nodes V, R, N, L,I, E, B, and the root node, slots are allocated to the wireless nodes V,R, N, L, I, E, B, and the root node, in the order mentioned.

When the slots are allocated in this manner, a latency t1 where datatransmitted by the wireless node V is relayed by the wireless node R isa few slots. Similarly, also in the subsequent respective wirelessnodes, latencies are a few slots. As a result, in the wireless meshnetwork in FIG. 5, a data transfer time where the data transmitted bythe wireless node V is transferred to the root node is within one frame.

In the wireless communication system according to the embodiment, slotsare allocated to the respective wireless nodes in the manner as in thewireless mesh network in FIG. 5. That is, an earlier slot in a frame isallocated to a wireless node located earlier in a pathway of datacommunication. The wireless node located earlier in the pathway of datacommunication refers to a downstream wireless node in uplink or anupstream wireless node in downlink.

To achieve such allocation of slots, in this embodiment, a rank value Rof a wireless node is set to a slot. The rank value R of a wireless nodeis the number of hops from the wireless node to the root node, namely,the number of data transmission.

FIG. 6 is a diagram describing a slot allocation method according to theembodiment. For example, in FIG. 6, a wireless node A has one hop to aroot node, and thus has a rank value of 1. A wireless node D has twohops to the root node, and thus has a rank value of 2. The largestnumber of hops in a wireless communication system in FIG. 6 is N, andthus, rank values of respective wireless nodes are one of the valuesfrom 1 to N.

In the embodiment, a plurality of slot groups is set in the frame, and arank value R is set to the respective slot groups. The slot group is aninterval including a plurality of consecutive slots. To prevent anoverlap of the respective slot groups, N (where N is the largest numberof hops) or more slot groups are set in the frame. For example, when theframe is time-divided into 300 slots with the largest number of hopsN=10, ten slot groups, each including 30 consecutive slots, can be set.Note that the number of slots included in the respective slot groups maybe the same or different.

The above-described rank value R is set to the respective slot groups.Methods of setting the rank value R are different between uplink anddownlink. FIG. 6 is a diagram showing the method of setting the rankvalue R for uplink transmission.

As shown in FIG. 6, in uplink, the larger rank value R is set to anearlier slot group in a frame, and the smaller rank value R is set to alater slot group. For example, a rank value N is set to a first slotgroup in the frame shown in FIG. 6, and a rank value 1 is set to a lastslot group.

On the other hand, the rank value R for downlink transmission is set tothe respective slot groups in the reversed order of that for uplink.That is, in downlink, the smaller rank value R is set to an earlier slotgroup in the frame while the larger rank value R is set to a later slotgroup.

In this embodiment, each slot is allocated to a wireless node having thesame rank value as the rank value R set to a slot group including theslot. For example, in uplink transmission, a slot included in the firstslot group, to which the rank value N for uplink is set (slot group forR=N), is allocated to one of wireless nodes K, L, and M, each having therank value N.

By allocating slots in this manner, an earlier slot in the frame can beallocated to a wireless node located in downstream in an uplink pathwayof data communication. Similarly, an earlier slot in the frame can beallocated to a wireless node located in upstream in a downlink pathwayof data communication.

That is, as in the wireless network in FIG. 5, an earlier slot in theframe can be allocated to a wireless node located earlier in the pathwayof data communication. Therefore, with the wireless communication systemaccording to the embodiment, in both uplink and downlink, data transfertime can be shortened to within one frame.

Hereinafter, a frame where only downlink or uplink transmission isperformed is referred to as a simplex communication frame and a framewhere both uplink and downlink transmission are performed is referred toas a duplex communication frame. The slot allocation method in thesimplex communication frame is as described above. Here, slot allocationmethods in the duplex communication frame will be further described withreference to FIGS. 7 to 10. FIGS. 7 to 10 are diagrams describing slotallocation methods in the duplex communication frame.

In this embodiment, in a duplex communication frame, when the rank valueR is given, a rank value R+1 for uplink and a rank value R−1 fordownlink are set to different slot groups. Similarly, when the rankvalue R is given, the rank value R−1 for uplink and the rank value R+1for downlink are set to different slot groups.

As a result, for example, only a rank value 5 for uplink is set to athird slot group in FIG. 7, and only a rank value 3 for downlink is setto a fourth slot group. Also, only a rank value 3 for uplink is set to aseventh slot group in FIG. 7, and only a rank value 5 for downlink isset to an eighth slot group. This is for preventing interference ofwireless signals between wireless nodes apart by 2 in the rank value.

For example, in a first slot group in the frame, a wireless node with arank value 7 and a wireless node with a rank value 1 simultaneouslytransmit wireless signals. However, since the wireless node with therank value 7 and the wireless node with the rank value 1 are apart,their wireless signals do not interfere with each other.

On the other hand, when, in the third slot group in the frame, awireless node with the rank value 5 and a wireless node with the rankvalue 3 simultaneously transmit wireless signals, since the wirelessnode with the rank value 5 and the wireless node with the rank value 3are close, their wireless signals may interfere with each other.

However, as shown in FIG. 7, when the rank value 5 for uplink and therank value 3 for downlink are set to different slot groups, the wirelessnode with the rank value 5 and the wireless node with the rank value 3transmit wireless signals at different timings, thereby preventinginterference of wireless signals. Therefore, degradation ofcommunication quality caused by interference of wireless signals can besuppressed.

Such method of setting rank values can be performed not only when thelargest number of hops N is an odd number as in FIG. 7 (N=7), but alsowhen the largest number of hops N is an even number as in FIG. 8 (N=8).

Moreover, when there is a possibility of interference of wirelesssignals even when the rank values are apart by 3, with the given rankvalue R, it is only necessary that the rank value R for uplink and rankvalues R+3 and R−3 for downlink be set to different slot groups. Thisallows for preventing interference of wireless signals between wirelessnodes apart by 3 in the rank value.

Moreover, although the rank value R for uplink and the rank value R fordownlink are set to different slot groups in FIGS. 7 and 8, the rankvalue R may be set to the same slot group as shown in FIGS. 9 and 10.

In this case, in a slot group to which the rank value R for uplink andthe rank value R for downlink are set, a wireless node having the rankvalue R performs uplink and downlink transmission simultaneously. Forexample, in the case of FIG. 9, a wireless node L having a rank value 4performs uplink transmission to a wireless node I and downlinktransmission to wireless nodes N and O simultaneously in a slotallocated to the wireless node L. Allocating the rank value R for uplinkand the rank value R for downlink to the same slot group allows forreducing the number of slot groups, thereby shortening a frame.

Next, a method of setting a transmission interval in the wirelesscommunication system according to the embodiment will be described withreference to FIG. 11. In this embodiment, as shown in FIG. 11, downlinktransmission is performed for every frame and uplink transmission isperformed for every M frames. M is any integer of 2 or more. That is, acycle of M frames, including one duplex communication frame and (M−1)simplex communication frames, is repeated.

In this wireless communication system, when time per frame is defined asF, the respective wireless nodes X perform downlink transmission with aninterval F and uplink transmission with an interval F×M. That is, theuplink transmission interval is set to be longer than the downlinktransmission interval. This is because it is assumed that sensor data istransmitted in uplink while control data of the wireless communicationsystem is transmitted in downlink.

Generally, sensor data is, as compared to control data, greater involume but less in transmission frequency required. Therefore,performing uplink and downlink transmission for every frame may causeissues such as: a transmission frequency of control data falls short; orsensor data is transmitted at a greater transmission frequency thanrequired, thereby increasing power consumption of the wirelesscommunication system.

Therefore, in this embodiment, the time F per frame is set such thatcontrol data can be transmitted at a required transmission frequency.For example, when it is required to transmit control data every 5minutes, the time F per frame is set to be 5 minutes or less.

Also, the uplink transmission interval is set to be longer as datavolume for uplink transmission is larger. That is, when the data volumefor uplink transmission is defined as v1, and data volume for downlinktransmission is defined as v2 (<v1), the larger the value of v1/v2 is,the larger M is set.

Setting uplink and downlink transmission intervals in this manner allowsfor meeting the required transmission frequency of the control datawhile reducing uplink transmission having large data volume, therebyreducing power consumption of the wireless communication device andsystem.

Note that, when the data volume for uplink transmission is smaller thanthe data volume for downlink transmission, uplink transmission can beperformed for every frame, and, downlink transmission can be performedfor every M frames. Moreover, when a transmission frequency required foruplink is greater than a transmission frequency required for downlink,the time F per frame can be set according to the transmission frequencyrequired for uplink.

Next, a configuration of the wireless communication device 1 included inthe wireless communication system according to the embodiment will bedescribed with reference to FIGS. 12 and 13. The wireless communicationdevice 1 according to the embodiment automatically achieves the slotallocation as described above. FIG. 12 is a diagram showing a functionalconfiguration of the wireless communication device 1. As shown in FIG.12, the wireless communication device 1 includes a transmission andreception antenna 11 and a wireless communication unit 12.

Hereinafter, the wireless communication device 1 is referred to as thepresent node. A wireless node that transmits data to the present node isreferred to as a source node. A wireless node to which the present nodetransmits data is referred to as a destination node. Also, a slot groupto which the rank value R is set is referred to as a slot group R.

The transmission and reception antenna 11 transmits or receives wirelesssignals. The transmission and reception antenna 11 converts the receivedwireless signals into electrical signals, and inputs the electricalsignals to the wireless communication unit 12. The transmission andreception antenna 11 converts electrical signals, output from thewireless communication unit 12, into wireless signals and transmits thewireless signals.

The wireless communication unit 12 includes a transceiver 13, adestination determiner 14, a relay data storage 15, a transmission datagenerator 16, a destination node determiner 17, a timer 18, a frame datastorage 21, and a sleep controller 22.

The transceiver 13 receives data from the source node. That is, thetransceiver 13 performs predetermined signal processing to theelectrical signals input from the transmission and reception antenna 11and obtains data. The signal processing includes analog-to-digitalconversion and decoding in accordance with a predetermined communicationprotocol. The data received by the transceiver 13 includes the rankvalue, a node ID, and relay data of the source node and a node ID of thedestination node.

A node ID is an identifier of each wireless communication deviceincluded in the wireless communication system. The relay data is datarelayed by the source node after being received from another wirelessnode. In uplink, the relay data includes sensor data. In downlink, therelay data includes control data. The destination node is a wirelessnode which is a destination of data transmitted by the source node.

FIG. 13 is a diagram describing operation timings of the transceiver 13.In FIG. 13, operation timings of a wireless node U having a rank value 7is shown.

In uplink, the transceiver 13 performs a reception operation during aslot group R+1 to which a rank value R+1 larger by 1 than the rank valueR of the present node is set. For example, the transceiver 13 of thewireless node U performs a reception operation during a first slot groupto which a rank value 8 for uplink is set. This allows the transceiver13 to receive data from a downstream wireless node including the childnode. Based on the data received from the child node, the transmissiondata generator 16 generates uplink transmission data.

Furthermore, in uplink, the transceiver 13 performs a receptionoperation during a slot group R−1 to which a rank value R−1 smaller by 1than the rank value R of the present node is set. For example, thetransceiver 13 of the wireless node U performs a reception operationduring a third slot group a rank value 6 for uplink is set. This allowsthe transceiver 13 to receive data from an upstream wireless nodeincluding the parent node. Based on the data received from the upstreamwireless node, the destination node determiner 17 updates the parentnode.

On the other hand, in downlink, the transceiver 13 performs a receptionoperation during a slot group R−1 to which the rank value R−1 smaller by1 than the rank value R of the present node is set. For example, thetransceiver 13 of the wireless node U performs a reception operationduring a ninth slot group to which a rank value 6 for downlink is set.This allows the transceiver 13 to receive data from an upstream wirelessnode including the parent node. Based on the data received from theparent node, the transmission data generator 16 generates downlinktransmission data.

In downlink, the transceiver 13 also performs a reception operationduring a slot group R+1 to which the rank value R+1 larger by 1 than therank value R of the present node is set. For example, the transceiver 13of the wireless node U performs a reception operation during an eleventhslot group to which the rank value 8 for downlink is set. This allowsthe transceiver 13 to receive data from a downstream wireless nodeincluding the child node. Based on the data received from the downstreamwireless node, the destination node determiner 17 updates the childnode.

Furthermore, the transceiver 13 transmits the transmission data to thedestination node. That is, the transceiver 13 performs predeterminedsignal processing to the transmission data generated by the transmissiondata generator 16, converts the transmission data into electricalsignals, and inputs the electrical signals to the transmission andreception antenna 11. The signal processing includes digital-to-analogconversion and encoding in accordance with a predetermined communicationprotocol. The transmission data includes the rank value, the node ID,and the relay data of the present node and the node ID of thedestination node.

In uplink, the transceiver 13 performs a transmission operation during atransmission slot included in a slot group R to which the same rankvalue R for uplink as the rank value R of the present node is set. Forexample, the transceiver 13 of the wireless node U performs atransmission operation during a transmission slot included in a secondslot group to which the rank value 7 for uplink is set. This allows thetransceiver 13 to relay, to the parent node, the data received from thechild node.

Also, in downlink, the transceiver 13 performs a transmission operationduring a transmission slot included in a slot group R to which the samerank value R for downlink as the rank value R of the present node isset. For example, the transceiver 13 of the wireless node U performs atransmission operation during a transmission slot included in a tenthslot group to which the rank value 7 for downlink is set. This allowsthe transceiver 13 to relay, to the child node, the data received fromthe parent node.

Note that, the transmission slot where the transceiver 13 performs thetransmission operation is determined from among a plurality of slotsincluded in the slot group R by a transmission slot determiner 20, whichwill be described later.

The destination determiner 14 obtains the data received by thetransceiver 13 and determines whether a destination of the received datais the present node. When the node ID of the destination node includedin the received data is the node ID of the present node, the destinationdeterminer 14 determines that the destination of the received data isthe present node.

The relay data storage 15 temporarily stores, as relay data, thereceived data, the destination of which has been determined as thepresent node by the destination determiner 14.

The transmission data generator 16 generates transmission data based onthe relay data stored in the relay data storage 15. The transmissiondata is generated by adding, to the relay data, data such as the rankvalue and the node ID of the present node. In uplink, sensor data of thepresent node, for example, is further added to the relay data. Thetransmission data generated by the transmission data generator 16 istransmitted by the transceiver 13 as described above.

The destination node determiner 17 determines the destination node ofthe transmission data based on the data received by the transceiver 13.In uplink, the destination node is the parent node and, in downlink, thedestination node is the child node. A node ID of the destination nodedetermined by the destination node determiner 17 is added to thetransmission data.

The destination node determiner 17, for example, refers to the rankvalue of the source node included in the data received by thetransceiver 13 and determines, as the parent node, a wireless nodehaving the highest wireless signal intensity among wireless nodes havingthe rank value smaller by 1 than the rank value of the present node.

The destination node determiner 17, for example, refers to the rankvalue of the source node included in the data received by thetransceiver 13 and determines, as the child node, a wireless node havingthe highest wireless signal intensity among wireless nodes having therank value larger by 1 than the rank value of the present node.

Alternatively, the destination node determiner 17, for example, mayrefer to the node ID of the destination node included in the datareceived by the transceiver 13 and determine, as the child node, awireless node, the destination of which is the present node.

The timer 18 determines a timing for the transceiver 13 to transmit thetransmission data, namely, the transmission slot, such that an uplinktransmission interval is longer than a downlink transmission interval.As shown in FIG. 12, the timer 18 includes a frame determiner 19 and atransmission slot determiner 20.

The frame determiner 19 determines a type of the current frame (duplexcommunication frame or simplex communication frame). The framedeterminer 19, for example, can determine whether the current frame isthe duplex communication frame by comparing a start time and a finishtime of the duplex communication frame with the current time. The starttime or the finish time of the duplex communication frame may be presetor be included in control data received in downlink.

The transmission slot determiner 20 determines the transmission slotbased on the frame type determined by the frame determiner 19 and framedata. The frame data is setting data of the frames, the slots, the slotgroups, etc. in the wireless communication system as described above.The frame data may be preregistered in the wireless communication device1 or registered and updated by means of wireless communication. Theframe data is stored in the frame data storage 21.

The transmission slot determiner 20 first obtains the determinationresult from the frame determiner 19. When the current frame is thesimplex communication frame, the transmission slot determiner 20 selectsthe slot group R for downlink based on the rank value R of the presentnode and the frame data. Next, the transmission slot determiner 20determines the transmission slot from among slots included in the slotgroup R.

When the current frame is the duplex communication frame, thetransmission slot determiner 20 selects the slot group R for downlinkand the slot group R for uplink based on the rank value R of the presentnode and the frame data. Next, the transmission slot determiner 20determines the transmission slot for uplink and the transmission slotfor downlink from among the slots included in the slot group R foruplink and the slot group R for downlink, respectively.

The transmission slot determiner 20, for example, may determine thetransmission slots from the slot groups R by using the node ID of thepresent node. Specifically, node IDs of respective wireless nodesincluded in the wireless communication system may be pre-allocated tothe slots in the respective slot groups, and the node IDs may be storedas the frame data in the frame data storage 21. For example, when thewireless communication system includes twenty wireless nodes having nodeIDs of 1 to 20, each slot group may be preset to include twenty slots towhich the node IDs of 1 to 20 are allocated. Then, the transmission slotdeterminer 20 is only required to determine, as the transmission slots,slots to which the node ID of the present node is allocated from slotgroups R. Note that a method to determine the transmission slot from theslot group R is not limited to the above.

Determination of the transmission slot by the timer 18 in such a mannerallows for allocating, to the wireless communication device 1, thetransmission slot corresponding to the rank value of the present node.As a result, the above-described slot allocation can be automaticallyachieved.

Note that the timer 18 may perform synchronization processing beforedetermining the transmission slot. The synchronization processing is tosynchronize a time counted in the present node with another wirelessnode.

The timer 18, for example, obtains a transmission time (transmissionslot) from the source node based on the rank value and the node ID ofthe source node included in the data received by the transceiver 13 andthe frame data. The timer 18 can perform the synchronization processingby comparing the sum of the transmission time and a signal processingtime at the transceiver 13 of the present node with the time counted inthe present node. Here, the synchronization processing may be performedby further adding time required for wireless signal propagation from thesource node.

The sleep controller 22 functions while power is supplied thereto,regardless of an operation state of the wireless communication unit 12.The sleep controller 22 counts time and controls an operation state ofthe transceiver 13 between a sleep state and an awake state based on thecounted time, the rank value of the present node, the frame data, andthe transmission slot determined by the transmission slot determiner 20.

The sleep state is a state where transmission or reception of data bythe transceiver 13 is halted. In the sleep state, since no transmissionor reception of data is performed, power consumption of the wirelesscommunication device 1 is reduced. The awake state is a state where thetransceiver 13 may transmit or receive data. Hereinafter, transition ofthe transceiver 13 from the awake state to the sleep state is referredto as “going to sleep” and transition from the sleep state to the awakestate is referred to as “waking up.”

The sleep controller 22 retains the transceiver 13 in the sleep statewhile the transceiver 13 does not transmit or receive data and retainsthe transceiver 13 in the awake state while the transceiver 13 transmitsor receives data. Specifically, the sleep controller 22 retains thetransceiver 13 in the awake state during the transmission slotdetermined by the transmission slot determiner 20. The sleep controller22 determines an interval where the transceiver 13 receives data basedon the counted time, the rank value of the present node, the frame data,and the transmission slot determined by the transmission slot determiner20 and retains the transceiver 13 in the awake state during receptionthereby. The sleep controller 22 retains the transceiver 13 in the sleepstate for other intervals.

Next, a hardware configuration of the wireless communication device 1will be described with reference to FIG. 14. As shown in FIG. 14, thewireless communication device 1 includes a computer 100. The computer100 includes a central processing unit (CPU) 101, an input device 102, adisplay device 103, a communication device 104, and a storage device105, which are connected to each other by a bus 106.

The CPU 101 is a control device and an arithmetic device of the computer100. The CPU 101 performs arithmetic processing based on data or aprogram input from the respective devices (e.g. the input device 102,the communication device 104, and the storage device 105) connectedthereto via the bus 106 and outputs the arithmetic result or controlsignals to the respective devices (e.g. the display device 103, thecommunication device 104, and the storage device 105) connected theretovia the bus 106.

Specifically, the CPU 101 executes an operating system (OS) of thecomputer 100 or a wireless communication program and controls therespective devices included in the computer 100. The wirelesscommunication program allows the computer 100 to implement theabove-described functional configurations of the wireless communicationunit 12. Execution of the wireless communication program by the CPU 101allows the computer 100 to function as the wireless communication device1.

The input device 102 inputs data to the computer 100. The input device102 may be, for example, a keyboard, a mouse, or a touch screen, but isnot limited thereto. Note that the wireless communication device 1 maybe configured without the input device 102.

The display device 103 displays an image or a projected image. Thedisplay device 103 may be, for example, a liquid crystal display (LCD),a cathode-ray tube (CRT), or a plasma display panel (PDP), but is notlimited thereto. The received data or the transmission data may bedisplayed on the display device 103. Note that the wirelesscommunication device 1 may be configured without the display device 103.

The communication device 104 allows the computer 100 to communicate withan external device (e.g. another wireless node) in a wireless or wiredmanner. The communication device 104 may be, for example, a modem, ahub, or a router, but is not limited thereto. Data such as the receiveddata, the transmission data, and the frame data may be input from anexternal device via the communication device 104. The transceiver 13 maybe configured by using the communication device 104. Also, thetransmission and reception antenna 11 may be included in thecommunication device 104.

The storage device 105 stores the OS of the computer 100, the wirelesscommunication program, data required for execution of the wirelesscommunication program, data generated upon execution of the wirelesscommunication program, etc. The storage device 105 includes a mainmemory and an external storage device. The main memory may be, forexample, a RAM, a DRAM, or an SRAM, but is not limited thereto. Theexternal storage device may be a hard disk, an optical disk, a flashmemory, or a magnetic tape, but is not limited thereto. The relay datastorage 15 or the frame data storage 21 may be configured by using thestorage device 105.

Note that the computer 100 may include one or more CPUs 101, inputdevices 102, display devices 103, communication devices 104, and storagedevices 105 or be connected to a peripheral device such as a printer ora scanner.

Furthermore, the wireless communication unit 12 may be configured by thesingle computer 100 or a system including the plurality of computers 100connected to each other.

Moreover, the wireless communication program may be prestored in thestorage device 105 of the computer 100, stored in a storage medium suchas a CD-ROM, or uploaded on the Internet. In any of these cases, byinstalling and executing the wireless communication program on thecomputer 100, the wireless communication device 1 can be configured.

Furthermore, a sensor such as a temperature sensor and an accelerationsensor may be connected to the computer 100 directly or via thecommunication device 104 in a wireless or wired manner.

Next, operations of the wireless communication device 1 according to theembodiment in the respective frames will be described with reference toFIGS. 15 to 21. Hereinafter, it is assumed that, at a starting point ofthe frame, the transceiver 13 is in the sleep state with the parent nodeand the child node having been determined. When a new frame starts, theframe determiner 19 first determines a type of the current frame. Thedetermination method is as described above.

First, operations of the wireless communication device 1 in the simplexcommunication frame will be specifically described with reference toFIGS. 15 and 16. FIG. 15 is a flowchart showing operations in a simplexcommunication frame. Hereinafter, it is assumed that the wirelesscommunication device 1 is a wireless node U having a rank value 7.

In step S1, the transmission slot determiner 20 determines a downlinktransmission slot from a slot group 7 for downlink, to which the rankvalue 7 of the present node is set. Thereafter, the wirelesscommunication device 1 stands by until a slot group 6 for downlinkstarts.

In step S2, the transceiver 13 receives data during the slot group 6 fordownlink. Specifically, when the slot group 6 for downlink starts, thesleep controller 22 wakes up the transceiver 13, and then, thetransceiver 13 initiates data reception. This allows the transceiver 13to receive data from an upstream wireless node having a rank value 6.With the data received by the transceiver 13, a destination node thereofis determined by the destination determiner 14, and the data transmittedfrom the parent node to the present node is stored in the relay datastorage 15. When the slot group 6 for downlink finishes, the transceiver13 terminates data reception, and the sleep controller 22 retains thetransceiver 13 in the sleep state.

In step S3, the destination node determiner 17 determines a new parentnode based on the data received by the transceiver 13 in step S2. Themethod of determining the parent node is as described above. As aresult, the parent node can be updated according to the latestcommunication state.

In step S4, the transmission data generator 16 generates thetransmission data based on the relay data stored in the relay datastorage 15. The method of generating the transmission data is asdescribed above. Then, the wireless communication device 1 stands byuntil the transmission slot determined in step S1 starts.

In step S5, the transceiver 13 transmits the transmission data to thechild node. Specifically, when the transmission slot for downlinkstarts, the sleep controller 22 wakes up the transceiver 13, and then,the transceiver 13 initiates transmission of the transmission data. Thisallows the data received from the parent node to be relayed to the childnode. When the transmission slot finishes, the transceiver 13 terminatesdata transmission, and then, the sleep controller 22 retains thetransceiver 13 in the sleep state. Also, the relay data stored in therelay data storage 15 is erased. Thereafter, the wireless communicationdevice 1 stands by until a slot group 8 for downlink starts.

In step S6, the transceiver 13 receives data. Specifically, when theslot group 8 for downlink starts, the sleep controller 22 wakes up thetransceiver 13, and then, the transceiver 13 initiates data reception.This allows the transceiver 13 to receive data from a downstreamwireless node having a rank value 8. When the slot group 8 for downlinkfinishes, the transceiver 13 terminates data reception, and then, thesleep controller 22 retains the transceiver 13 in the sleep state.

In step S7, the destination node determiner 17 determines a new childnode based on the data received by the transceiver 13 in step S6. Themethod of determining the child node is as described above. As a result,the child node can be updated according to the latest communicationstate. Thereafter, the wireless communication device 1 stands by until anext frame starts.

Next, operations of the wireless communication device 1 in a duplexcommunication frame will be specifically described with reference toFIGS. 17 and 18. FIG. 17 is a flowchart showing operations in a duplexcommunication frame.

In step S1, the transmission slot determiner 20 determines a downlinktransmission slot from a slot group 7 for downlink, to which the rankvalue 7 of the present node is set. Furthermore, the transmission slotdeterminer 20 determines an uplink transmission slot from a slot group 7for uplink, to which the rank value 7 of the present node is set.

Next, in step S8, the transceiver 13 receives data during a slot group 8for uplink. Specifically, when the slot group 8 for uplink starts, thesleep controller 22 wakes up the transceiver 13, and then, thetransceiver 13 initiates data reception. This allows the transceiver 13to receive data from a downstream wireless node having a rank value 8.With the data received by the transceiver 13, a destination node thereofis determined by the destination determiner 14, and the data transmittedfrom the child node to the present node is stored in the relay datastorage 15. When the slot group 8 for uplink finishes, the transceiver13 terminates data reception, and then, the sleep controller 22 retainsthe transceiver 13 in the sleep state.

In step S9, the destination node determiner 17 determines a new childnode based on the data received by the transceiver 13 in step S8. Themethod of determining the child node is as described above. As a result,the child node can be updated according to the latest communicationstate.

In step S10, the transmission data generator 16 generates thetransmission data based on the relay data stored in the relay datastorage 15. The method of generating the transmission data is asdescribed above. Thereafter, the wireless communication device 1 standsby until the uplink transmission slot determined in step S1 starts.

In step S11, the transceiver 13 transmits the transmission data to theparent node. Specifically, when the uplink transmission slot starts, thesleep controller 22 wakes up the transceiver 13, and then, thetransceiver 13 initiates transmission of the transmission data. Thisallows the data received from the child node to be relayed to the parentnode. When the transmission slot finishes, the transceiver 13 terminatesdata transmission, and then, the sleep controller 22 retains thetransceiver 13 in the sleep state. Also, the relay data stored in therelay data storage 15 is erased. Thereafter, the wireless communicationdevice 1 stands by until a slot group 6 for uplink starts.

In step S12, the transceiver 13 receives data. Specifically, when theslot group 6 for uplink starts, the sleep controller 22 wakes up thetransceiver 13, and then, the transceiver 13 initiates data reception.This allows the transceiver 13 to receive data from an upstream wirelessnode having a rank value 6. When the slot group 6 for uplink finishes,the transceiver 13 terminates data reception, and then, the sleepcontroller 22 retains the transceiver 13 in the sleep state.

In step S13, the destination node determiner 17 determines a new parentnode based on the data received by the transceiver 13 in step S12. Themethod of determining the parent node is as described above. As aresult, the parent node can be updated according to the latestcommunication state. Thereafter, the wireless communication device 1stands by until the slot group 6 for downlink starts.

When the slot group 6 for downlink starts, the processing of steps S2 toS7 is performed. The steps S2 to S7 are the same as the operations inthe simplex communication frame.

As described above, by setting uplink and downlink transmissionintervals according to data volume to be transmitted, the wirelesscommunication device 1 and system according to the embodiment can meet arequired transmission frequency while reducing a frequency of uplinktransmission having large data volume, thereby reducing powerconsumption.

Moreover, in the wireless communication system, an earlier slot in aframe is allocated to a wireless node located earlier in a pathway ofdata communication, thereby shortening a data transfer time to withinone frame. Furthermore, the wireless communication device canautomatically achieve the slot allocation as described above.

Note that, in the above description, it has been assumed thattransmission in the first direction is uplink transmission andtransmission in the second direction is downlink transmission. However,when data volume for uplink transmission is smaller than data volume fordownlink transmission, the directions may be vice versa. In this case,preferably, uplink transmission is performed for every frame anddownlink transmission is performed for every M frames.

Also, as shown in FIG. 19, in the duplex communication frame, thetransceiver 13 may not perform the reception processing (step S6) duringa slot group R+1 for downlink. In this case, updating the child node maybe performed based on the data received in the reception processing(step S8) during a slot group R+1 for uplink.

Similarly, the transceiver 13 may not perform the reception processing(step S12) during a slot group R−1 for uplink in the duplexcommunication frame. In this case, updating the parent node may beperformed based on data received in the reception processing (step S2)during a slot group R−1 for downlink.

Also, as shown in FIG. 20, in a simplex communication frame, thetransceiver 13 may not perform the reception processing (step S6) duringthe slot group R+1 for downlink. In this case, preferably, updating thechild node is performed not in the simplex communication frame but inthe duplex communication frame.

Furthermore, as shown in FIG. 21, in the simplex communication frame,the transceiver 13 may alternatively perform reception processing onlyduring a transmission slot of the parent node, instead of performing thereception processing during the slot group R−1 for downlink (step S2).In this case, preferably, updating the parent node is performed not inthe simplex communication frame but in the duplex communication frame.

As described above, reducing the interval where the transceiver 13performs reception processing and increasing the interval of the sleepstate allow for further saving the power of the wireless communicationdevice 1 and system.

(Second Embodiment)

Next, a wireless communication device and system according to a secondembodiment will be described with reference to FIGS. 21 to 25. In thisembodiment, a wireless communication device 1 has a plurality ofoperation states in a simplex communication frame. The operation statestransit from one state to another depending on success or failure ofreception. The other configurations are the same as those in the firstembodiment. Operations of the wireless communication device 1 in asimplex communication frame will be described below.

FIG. 22 is a state transition diagram showing transition among operationstates of the wireless communication device 1 according to theembodiment in a simplex communication frame. As shown in FIG. 22, thewireless communication device 1 has three operation states of states 1to 3. Among the respective states, a transceiver 13 has differenttimings for performing reception processing.

As shown in FIG. 21, state 1 is an operation state where the transceiver13 receives data only during a transmission slot of a parent node. Instate 1, the parent node and a child node are not updated. In state 1,since an interval, where the wireless communication device 1 is awake,is the shortest (two slots), power consumption of the wirelesscommunication device 1 is minimized.

As shown in FIG. 22, when the transceiver 13 succeeds in receptionduring the transmission slot of the parent node, the operation state ofstate 1 continues. That is, the wireless communication device 1 operatesin state 1 also in a next simplex communication frame.

However, wireless communication is not always successful due to itsnature and may fail because of fading or shadowing. Fading is aphenomenon where reception power drops due to time-dependent variationsof wireless signals. This occurs, for example, when wireless signals areweakened due to transfer of a wireless node, and required power relativeto noise is no longer obtained. Meanwhile, shadowing is a phenomenonwhere reception power drops due to an obstacle existing between wirelessnodes.

Therefore, as shown in FIG. 22, when the transceiver 13 fails inreception during the transmission slot of the parent node, the operationstate transits from state 1 to state 2.

State 2 is an operation state where the transceiver 13 continuesreception until a transmission slot of the present node starts. When, instate 1, the wireless communication device 1 has failed in reception atthe end of the transmission slot of the parent node, the wirelesscommunication device 1 transits to state 2 without transiting to thesleep state.

As shown in FIG. 23, when the transceiver 13 has succeeded in receptionfrom another wireless node before the transmission slot of the presentnode starts, the transceiver 13 terminates reception and goes to sleep.The wireless communication device 1 then determines, as a new parentnode, the wireless node from which the wireless communication device 1has succeeded in reception. In the case of FIG. 23, the parent node isupdated from a wireless node R to a wireless node S. Also, transmissiondata is generated based on data successfully received.

In this manner, when reception succeeds in state 2, the operation statetransits from state 2 to state 1. That is, the operation state of thewireless communication device 1 in the next simplex communication frameis state 1.

On the other hand, as shown in FIG. 24, when the transceiver 13 hasfailed in reception from other wireless nodes before the transmissionslot of the present node starts, the wireless communication device 1transmits the transmission data during the transmission slot of thepresent node. This transmission data does not include relay data fromthe parent node. In this manner, when reception fails in state 2, theoperation state transits from state 2 to state 3. That is, the operationstate of the wireless communication device 1 in the next simplexcommunication frame is state 3.

As shown in FIG. 25, state 3 is an operation state where the transceiver13 receives data during a slot group including the transmission slot ofthe parent node, namely, a slot group R−1 for downlink.

In state 3, when the transceiver 13 has succeeded in reception fromother wireless nodes in the slot group R−1, the wireless communicationdevice 1 determines the new parent node from among the wireless nodesfrom which the wireless communication device 1 has succeeded inreception. Also, the transmission data is generated based on the datareceived from the new parent node.

In this manner, when reception succeeds in state 3, the operation statetransits from state 3 to state 1. That is, the operation state of thewireless communication device 1 in the next simplex communication frameis state 1.

On the other hand, when the transceiver 13 has failed in reception fromother wireless nodes in the slot group R−1, the wireless communicationdevice 1 transmits the transmission data during the transmission slot ofthe present node. This transmission data does not include the relay datafrom the parent node. In this manner, when the reception fails in state3, the operation state of state 3 continues. That is, the operationstate of the wireless communication device 1 in the next simplexcommunication frame is state 3.

Note that, in state 3, the transceiver 13 may perform the receptionoperation during a plurality of slot groups or the whole frame, not onlyduring the slot group R−1, and determine the new parent node.

As described above, the wireless communication device 1 according to theembodiment continues operation in state 1 when in a preferablecommunication state. This allows for reducing power consumption of thewireless communication device 1. Alternatively, even when the receptionfails, operating in state 2 or state 3 allows for determining the newparent node, thereby retaining communication.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

The invention claimed is:
 1. A wireless communication device comprising:a transceiver configured to transmit and receive data and transmit thedata to a first node in a first direction, and transmit the data to asecond node different from the first node in a second direction, and atimer configured to determine a timing for the transceiver to transmitthe data in each of the first direction and the second direction suchthat a transmission interval in the first direction is longer than atransmission interval in the second direction, wherein the timer isimplemented by a processor and the processor is configured to determinewhether a current frame is a duplex communication frame in whichtransmission in the first direction and the second direction isperformed, or a simplex communication frame in which transmission in thesecond direction is performed; and determine a transmission slot, inwhich the transceiver transmits the data, from the frame time-dividedinto a plurality of slots, based on a rank value of a present nodecorresponding to the number of hops to a root node.
 2. The deviceaccording to claim 1, wherein data volume transmitted in the firstdirection is larger than data volume transmitted in the seconddirection.
 3. The device according to claim 1, wherein the transmissionintervals in the first direction and the second direction are setaccording to data volume transmitted in the first direction and thesecond direction.
 4. The device according to claim 1, whereintransmission in the first direction is uplink transmission, andtransmission in the second direction is downlink transmission.
 5. Thedevice according to claim 1, wherein the transceiver is configured totransmit the data in the first direction for every M frames (where M isan integer of 2 or more) and in the second direction for every frame. 6.The device according to claim 1, wherein a plurality of slot groupsincluding a plurality of consecutive slots is set to the frame, rankvalues different from each other are set to the respective slot groups,and the processor is configured to determine the transmission slot fromamong slots included in a slot group to which the rank value of thepresent node is set.
 7. The device according to claim 6, wherein rankvalues for transmission in the first direction and rank values fortransmission in the second direction are set to the frame.
 8. The deviceaccording to claim 7, wherein a larger rank value for transmission inthe first direction is set to an earlier slot group.
 9. The deviceaccording to claim 7, wherein a smaller rank value for transmission inthe second direction is set to an earlier slot group.
 10. The deviceaccording to claim 7, wherein, in the duplex communication frame, a rankvalue R+1 for the first direction and a rank value R−1 for the seconddirection are set to different slot groups.
 11. The device according toclaim 6, wherein, in the simplex communication frame, the transceiverreceives the data during a slot group to which a rank value smaller by 1than a rank value of the present node is set.
 12. The device accordingto claim 6, wherein, in the simplex communication frame, the transceiverreceives the data during a transmission slot of a parent node.
 13. Thedevice according to claim 12, wherein, when the transceiver has failedin reception of the data in the transmission slot of the parent node,the transceiver continues reception of the data until a transmissionslot of the present node starts.
 14. The device according to claim 13,wherein, when the transceiver has failed in reception of the data beforethe transmission slot of the present node starts, in a next simplexcommunication frame, the transceiver receives the data during a slotgroup including the transmission slot of the parent node.
 15. The deviceaccording to claim 1, further comprising a sleep controller configuredto halt transmission and reception of the data by the transceiver.
 16. Awireless communication system comprising: the device according to claim1; and a concentrator, implemented by a computer, configured toconcentrate the data from the device.